Overview of Aluminum Hydroxide Flame Retardants
Among the broad spectrum of available options, aluminum hydroxide (Al(OH)3, ATH) has emerged as a versatile and widely utilized flame retardant. ATH has found extensive applications across various industries. Its versatility allows for incorporation into polymers, textiles, cables, paints, and coatings.
ATH provides flame retardancy through several interrelated mechanisms. Its endothermic decomposition absorbs heat from the surrounding environment, thereby reducing the temperature of the material. The released water vapor dilutes the oxygen concentration, suppressing the combustion process. Additionally, the formation of a protective char layer acts as an insulator, preventing the propagation of the flame.
Synergistic Flame Retardant System of Aluminum Hydroxide
ATH synergistic flame retardant systems involve the combination of aluminum hydroxide and other flame retardant additives to enhance its flame retardant properties. There are many compounds that have been shown to exhibit synergistic flame retardant effects with aluminum hydroxide, including but not limited to halogenated compounds (brominated or chlorinated flame retardants), phosphorus compounds, and nitrogen-based compounds (melamine, melamine derivatives, or guanidine compounds) etc., just to name a few:
- Aluminum hydroxide and organic boron flame retardants can be used for synergistic flame retardancy of polyethylene.
- Aluminum hydroxide, red phosphorus, and expandable graphite are synergistic flame retardants for polyethylene.
- The synergistic flame retardant effect of aluminum hydroxide and ammonium polyphosphate on epoxy resin.
- Aluminum hydroxide and melamine cyanurate (MCA) synergistically flame retardant ethylene vinyl acetate (EVA).
EVA-ATH-MCA composite material. [1]
Nano Aluminum Hydroxide Flame Retardant Systems
Nano-ATH has emerged as a promising FR additive due to its unique properties, such as high surface area, tunable particle size, excellent thermal stability, and low toxicity.
Nano-ATH can be synthesized through various methods, such as precipitation, sol-gel, hydrothermal, and template-assisted approaches. These methods allow precise control over particle size, shape, and surface properties, enabling tailoring of the final flame retardant system for specific applications. For example, Sherif Elbasuney fabricated nanoscale ATH particles via a continuous hydrothermal method and developed self-extinguishing multi-component epoxy nanocomposites that can withstand direct flame sources at 1700 °C.
The continuous hydrothermal synthesis of ATH. [2]
Nano-ATH can also be added to the composite foaming agent solution to prepare nano-ATH foam with good formability and high stability, which can be used to prevent spontaneous combustion of coal in goaf areas. Research shows that the nano-ATH foam can extend the time to ignition (TTI) value of coal samples to 176 s. In addition, the continuous combustion time was shortened to 211 s, the peak heat release dropped to 58 kW/m2 and the peak smoke production rate dropped to 0.0049 m2/s, showing good flame retardant and smoke suppression performance of nano-ATH.
Nano-ATH for preventing spontaneous coal combustion. [3]
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References
- Xu S, et al. Journal of Colloid and Interface Science, 2021, 589, 525-531.
- Elbasuney S. Powder Technology, 2017, 305, 538-545.
- Zhang L, et al. Fuel, 2021, 304, 121494.
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